Zero drag vertical &#34;i&#34; antenna



Sept. 14, 1954 J.A.A1.BANO 2,689,302

ZERO DRAG VERTICAL "I" ANTENNA Filed June 20. 1950 g PQ/MAIEY HN I 5 3 o A? 7 j El-2- fr0/V04? Y F//V 15 JNVENTOR.

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Patented Sept. 14, 1954 UNITED STATES PATENT OFFICE (Granted under-Title 35, U. S. Code (1952),

sec. 266) The invention described herein may be manufactured and used by or for the United States Government for governmental purposes without payment to me of any royalty thereon.

This invention relates to antennas with zero Wind drag faired into the skin of high speed aircraft.

An object of the present invention is to provide an improved zero drag antenna having a uniform omni-directional pattern of uniform intensity in the plane of the surface into which it is faired.

Another object is to provide an antenna adapted for operation in a range of frequencies comparable with the size of the antenna.

Another object is to provide an antenna mounted fiush with the skin of an aircraft to minimize wind drag on the antenna and such that operational parts of the antenna are disposed Within the fuselage and are sealed to minimize atmospheric effects upon the operating characteristics of the antenna.

With the above and other objects in view, as set forth hereinafter, an illustrative embodiment of the present invention is shown in the accompanying drawing within:

Fig. 1 is a plan View of an antenna embodying the present invention and with parts broken away and in section;

Fig. 2 is a section taken along the line 2 2 of Fig. l viewedY in the direction indicated by the arrows;

Fig. 3 is an axial sectional view of the pattern of the antenna shown in Figs. 1 and 2; and

Fig. 4 is a fragmentary section taken along the line 4-4 of Fig. 1.

The antenna shown in the accompanying drawing is principally of metal and comprises an outer hollow preferably cylindrical portion I, coaxial with an inner hollow preferably cylindrical portion 2 joined by and preferably integral with a base plate or a connecting base 3. An insulator 4 of low loss dielectric material positioned within the inner cylindrical portion 2 supports a center or inner conductor 5 positionedv coaxially and centrallyv of the inner cylindrical portion 2. The inner conductor 5 continues outwardly in an enlarged portion or boss 6 and inwardly in a coaxial line fitting inner connector 1. A coaxial line fitting outer connector 8 continues in a flange 9 by which it is secured to the base 3 of the antenna by means of screws IU'. A circular disk top loading plate II of the antenna is secured to the unattached end of the inner conductor boss 6 by al screw I2 or the like.

The cup shaped cavity of the antenna preferably is divided into quadrants by eight ns aligned axially in pairs and with the two ns in each pair spaced axially from each other a predetermined distance. A set of 4 primary fins I5 to I8, inclusive, are positioned at the mouth of the cupshaped cavity of the antenna and extend radially thereof with their opposite ends secured by welding, solder or the like, to the center or inner conductor boss 6 and to the inner surface of the outer cylindrical portion I. A set of 4 secondary nns I5 to I8', inclusive, are aligned axially with the four primary ns I5 to I8, inclusive, and are positioned in the bottom of the antenna cup-shaped cavity where they are attached by welding, solder or the like, to the inner surfaces of the antenna outer cylindrical portion I, to the inner cylindrical portion 2 and to the antenna base 3.

A closure plate, such as a plastic disk 20 closes the cup-shaped cavity of the antenna against the admission of water, dust and the like, by being mounted in and cemented to a rabbeted groove 2| in the outer edge of the antenna outer cylindrical portion I. Being so mounted, the plastic disk 20 continues in the plane of the skin 22 of the aircraft to provide a uniformly level outer surface that is substantially unbroken in the proximity of the antenna. The plastic disk 20 preferably overlies the antenna top plate I I. In this manner the present zero drag antenna is housed entirely within the aircraft fuselage with nothing projecting above the skin of the aircraft. With the electrically open end of the antenna so sealed by the disk 20, moisture and dust are excluded from the interior of the antenna thereby making the functional characteristics of the antenna reproducable and independent of weather conditions. The antenna cavity may be left open, however, without affecting its theoretical electrical characteristics.

The antenna assembly is supported firmly with respect to the skin 22 of the aircraft as by a broken ring 23 or the like. The ring 23 extends around and grips the antenna assembly by means of a ring collapsing screw 24. The collapsing screw 24 is positioned in a tangential hole in the broken ring 23 with its head bearing against a shoulder in one of the free ends of the ring and'- a threaded shaft of the screw 24 engaging threads in the other free end of the ring 23. The broken ring 23 is drilled with screw holes 26 at a desired' number of positions for the reception of retaining or mounting screws 25 that pass through the aircraft skin 22 and thread into the broken? ring 23.

The heads of the mounting screw 25 preferably?- are flush-mounted into the aircraft skin 22 so that they do not project above the skin 22.

The antenna shown in Figs. l and 2 of the drawing has a symmetrical radiation pattern 23 that is shown in section in Fig. 3, With a conical core 29 of silence, or no signal, at its center. Mounted as a zero drag antenna at the top, or at the bottom of an aircraft, the antenna is essentially vertically polarized and provides a uniform omnidirectional pattern in the azimuthal plane with a maximum contribution to a surface wave that extends at substantially low angles. The signal intensity in the horizontal direction is of an intensity that is substantially one-fourth of the maximum signal intensity. The horizontal signal intensity is indicated in Fig. 3 by that portion of the signal pattern 28 that is radiated above the aircraft skin 22' that represents the bottom of an aircraft into which the antenna is faired. The described signal pattern of the present antenna permits signals to be received up to the limits of the line of sight or of the horizon. The pattern, polarization and the voltage standing wave ratio of the present zero drag antenna are comparable tc those of a quarter wave length protruding type of antenna. Y

The center conductor and the top loading plate I I of the antenna are fed at the coaxial line fitting inner connector l from the inner or center conductor of a representative 50 ohm section of coaxial line, not shown, The outer extremities of the primary and the secondary fins, through the antenna outer cylindrical portion I and plate 3, together with the outer portion 8 of the coaxial line fitting at the base of the antenna are grounded directly to the aircraft skin 22. The antenna is adapted for transmission illustratively in the S band of frequencies. The fins act as an impedance match in sections that improve the antenna radio efficiency, since the top loading plate Il is coplanar with the radially extending primary fins I5 to I8, inclusive, at the surface o! the cavity and since both the primary fins and the secondary fins I5' to I8 inclusive, are secured at their radially outer ends to the antenna outer cylindrical portion I that is grounded to and Iin direct electrical connection with the aircraft skin 22. The secondary iins, through the antenna inner cylindrical portion 2, are insulated at their radially inner end by the insulator 4 from the center conductor 5 that leads from the coaxially line fitting center conductor I to the top loading plate II at the surface of the antenna cavity. The coaxial line fitting inner connector 1 is connected through the inner conductor 5, boss 6, top loading plate Il and primary ns I5 to I8, inclusive, with the ships skin 22. The coaxial line fitting outer connector 8 is connected through the coaxial line fitting outer connector flange 9, the antenna base plate 3 and the antenna outer cylindrical portion I, with the ships skin 22.

During transmission with the antenna operating at resonance, a potential difference exists between the narrow primary fins I5 to I8, inclusive, at the mouth of the cavity and the secondary fins I5' to IB, inclusive, secured to the antenna cavity base 3. This potential difference creates an electrical field that determines the antenna pattern and that radiates a radio frequency eld. The antenna pattern 28, as previously stated, is omni-directional in a horizontal plane and approaches vertical polarization with a conical zone of silence 29 at its center. The antenna pattern of the zero drag antenna ex- 'inductance tends in all horizontal directions beyond its conlcal zone of silence. The zero drag antenna has been proven experimentally to be usable in the S band over a range of 25 hundred to 43 hundred megacycles frequency band width. The zero drag antenna comprises electrically an inductance and a condenser connected in vseries and connected in parallel with an vantenna radiation impedance.

The antenna top loading plate I I concentrates capacity at the open mouth of the antenna, which simulates the antenna length of a stub antenna when operating at resonance. The top loading plate II, with the radially extended primary fins I5 to I 8, inclusive, acting in continuity of the function of the top loading plate Il, provides an antenna that is in the nature of a folded top antenna. The secondary ns I5 to I8 inclusive, that are secured to the antenna base 3, serve as an impedance matching means and increase the magintude of the signals transmitted from the antenna. The top loading plate II has the eect of increasing the electrical diameter of the antenna cavity without increasing its physical dimension, thereby lowering the output frequency range of the antenna.

Preferably, the antenna top loading plate II is approximately one-fourth wave length in diameter, with the wave length selected at a frequency in the center of the selected operating frequency range of the antenna. This diameter dimension of the top loading plate I I is not particularly critical. As previously stated, the top loading plate I I acts electrically as a. capacitance. The primary and the secondary i'lns act as an This capacitance-inductance relation forms a series circuit which is in parallel with the antenna radiation impedance. This capacitance-inductance relation has the e'ect of creating an improved impedance match between the antenna and a feeder system, such as a 50 ohms transmission line, for example (not shown) which carries power from a generator (not shown) to the antenna. The 50 ohm transmission line is attached to the antenna connector fitting 1-8 positioned below the base of the antenna cavity. The radiation pattern 28 represented in Fig. 3, as being radiated from the antenna shown in Figs. 1 and 2 of the drawing, is the result of a potential difference or a voltage that appears across the primary fins at the mouth of the antenna cavity and the secondary fins within the antenna cavity.

'Ihe present zero drag antenna canbe made to operate in any range of frequencies depending upon its size. The dimensions of the antenna are determined by the particular range of frequencies over which the antenna is intended t0 operate. The dimensions of the present antenna are not particularly critical. It has been found empirically and experimentally however, that a definite association exists between the antenna dimensions and the range of frequencies with which the antenna is to be used in order that uniform electrical characteristics may be obtained in the performance of the antenna.

In the designing of the antenna it is best to refer its dimensions to the center frequency `of the operating range of frequencies with which it is to be used. With reference to such a center frequency of the S band of frequencies worked in experimentally, the antenna cavity preferably is three-quarters of a wave length in diameter, its depth is one-quarter of a wave length. and the space between the primary ns and the secondary fins is one-sixteenth of a wave length.

band Width= X 100 expressed in percentage. In the above formula Fh is the upper limit of the frequency range and F1 is the lower limit of the frequency range.

The operation of the antenna is modified but is not lost in the absence of the top loading plate H. The pattern of the antenna loses its symmetry in the absence of two pairs of axially registering primary and secondary ns, such as the absence of ns' I1 and l1 and I8 and i8', but the antenna would continue to be operative within its altered pattern.

It is to be understood that the antenna that is shown and described herein has been submitted as an illustrative and operative embodiment of the present invention and that similarly operating parts and modifications thereof may be substituted therein without departing from the scope of the present invention.

What I claim is:

1. An antenna, comprising an electrically conductive hollow outer member, an electrically conductive base at one end of said hollow outer member, a coaxial line fitting hollow outer connector attached to said base, an electrically conductive hollow inner member attached tol said base, a coaxial line fitting inner conductor extending axially in both said tting outer connector and said inner member, insulator means between said conductor and said hollow inner member, a plurality of electrically conductive primary fins extending radially from said inner conductor to said outer member, and a plurality of electrically conductive secondary iins extending radially from said inner member to said outer member and spaced from said primary ns axially of said outer member.

2. The antenna dened in claim l with a top` loading plate attached to said inner conductor adjacent said primary ns.

3. The antenna defined in claim 1 with an electrically nonconductive closure plate closing said hollow outer member remote from said base.

4. The antenna deiined in claim 1 for use in a particular frequency range having a mid-frequency of a determined wave length and wherein said outer member is three-quarters of said wave length in diameter and one-quarter of said wave length in depth and wherein the primary and secondary ns are spaced apart one-sixteenth of said wave length.

5. The antenna defined in claim 1 faired into the skin of an aircraft and secured therein by means, comprising a circumferentially intern yrupted broken ring, a collapsing screw in said ring and binding said ring against said antenna outer member, and a plurality of mounting screws securing said ring to and inwardly of the skin of the aircraft.

6. A flush mounted antenna fed from a coaxial line having inner and outer` conductors, comprising an outer cylindrical antenna portion, an inner cylindrical antenna portion, an antenna base plate connecting said outer and inner cylin4 drical antenna portions, with the coaxial line outer conductor, a plurality of antenna primary iins disposed between said outer and inner cylindrical antenna portions, a plurality of antenna secondary ns disposed between said outer and inner cylindrical antenna portions and spaced axially from and separately aligned in pairs with said primary fins, an antenna inner conductor means extending axially of and insulated from said inner cylindrical antenna portion and enlarged at its outer end in a boss connected with the inner ends of said antenna primary fins.

References Cited in the le 0f this patent UNITED STATES PATENTS Number Name Date 2,235,506 Schelkunoi Mar. 18, 1941 2,269,821 Kemphert Jan. 13, 1942 2,368,663 Kandoian Feb. 6, 1945 2,414,266 Lindenblad Jan. 14, 1947 2,468,751 Hansen May 3, 1949 2,480,186 Gilbert Aug. 30, 1949 2,501,020 Barnes Mar. 21, 1950 2,508,085 Alford May 16, 1950 2,519,603 Reber Aug. 22, 1950 2,549,143 Tinus Apr. 17, 1951 

